Compressor runs and loads, but pressure stays below setpoint: often caused by leaks, restrictions, or capacity issues.
Key thing to distinguish here is pressure at compressor (or in compressor room) vs pressure at point of use. Check both. If the pressure at the point of use is too low, but the pressure in the compressor room is good, then your problem is "pressure drop".
What this problem usually means
When a rotary screw compressor runs and loads normally but can't reach or maintain the pressure setpoint, the problem is usually one of three things: air is escaping (leaks), airflow is restricted somewhere in the system, or demand exceeds compressor capacity.
Unlike a "won't load" problem where the inlet valve doesn't open at all, here the compressor IS compressing air -it just can't keep up or can't build to full pressure.
Check these first
5–10 minute checks before diving deeper
- Check for obvious air leaks: listen for hissing sounds near fittings, hoses, and connections
- Is the air demand higher than usual? (new equipment, additional users, leaky tools)
- Check inlet air filter: clogged filter reduces capacity significantly
- Verify the pressure setpoint hasn't been changed accidentally
- Check separator element differential pressure: high DP means clogged separator
- Listen for inlet valve modulating: it should be fully open when trying to reach setpoint
- Check discharge pressure reading vs. plant pressure: big difference means restriction in piping
- Look at compressor running hours vs. capacity: is it running 100% but still losing pressure?
- Check and replace downstream compressed air filters if installed: clogged filters add restriction
Common root causes
Why this happens in general compressors
- Air leaks in the system Leaks at fittings, hoses, quick disconnects, regulators, or downstream equipment. A single 3mm leak can waste 10+ CFM.
- Clogged inlet air filter Dirty inlet filter restricts airflow into the compressor, reducing capacity by 10-30% in severe cases.
- Separator element clogged High pressure drop across separator restricts discharge flow. Check differential pressure gauge: should be under 1 bar.
- Demand exceeds capacity System air demand has grown beyond what the compressor can supply. Common when facilities add equipment over time.
- Inlet valve not fully opening Inlet valve partially stuck or modulating incorrectly: compressor can't draw full capacity of air.
Don't increase the pressure setpoint to "compensate" for low pressure, this masks the real problem, increases energy consumption, and can cause other issues. Find and fix the root cause instead.
Compressed air at system pressure (7-13 bar) can cause injury. Never search for leaks by running your hand along pressurized lines: use soapy water or an ultrasonic leak detector.
Still stuck?
If the checks above haven't pointed at the cause, post your symptoms in the Q&A. Real-world answers, no sales pitch.